A substantial amount of the data used in digital terrain models comes
from analog maps (this includes a lot of the data developed for DMA).
The digital data can be no better than the original map data. Even for
parts of the U.S., some of this is old and inaccurate. I seem to recall
that the New Zealand sightseeing crash in Antartica some years ago
arose out of bad terrain data and there was at least one case where
a Navy bird flew into the Coast Range in California due to a "missing
mountain."
Of course the thing that matters is the vertical distance between you
and the actual terrain and there are some new instruments (laser altimeters
for example) that do this with high accuracy.
--
Duane F. Marble E-mail: marble.1@osu.edu
Department of Geography Telephone: (614) 292-2250
The Ohio State University Fax: (614) 292-6213
Columbus, Ohio 43210 Home Page: http://thoth.sbs.ohio-state.edu